18/6.] MR. E. R. ALSTON ON THE ORDER GLIRES. /3 



noted that they have no true alisphenoid canal, but a carotid canal 

 is present in the tympanic*. The optic foramina are confluent; and 

 the bony palate is reduced to a mere bridge between the molar series, 

 being bounded in front by the large confluent incisive foramina, and 

 behind bv the deep posterior emargination. The fibula is ankylosed 

 below with the tibia, and articulates with the calcaneum. There are 

 no vesicular glands ; and the testes are permanently external. 



The two families Leporid<e and Lagomyidce are certainly very 

 nearly allied, but differ in several important characters ; and I have 

 therefore followed Professor Lilljeborg in keeping them distinct. 

 The absence of postorbital frontal processes, the posterior continua- 

 tion of the zygoma towards the auditory meatus, the absence of 

 reticulation in the facial portion of the maxillary, and the full 

 development of the clavicles in the Pikas are among the points in 

 which their anatomy confirms their distinction from the Hares, out- 

 wardly indicated by the different proportion of their ears and tails. 



The remark has been made above that palaeontology has hitherto not 

 yielded much of interest to the student of this order. A striking ex- 

 ception, however, is to be found in certain wonderful forms from the 

 South- American Miocene and Pliocene, of which the true position has 

 been much disputed. Of these the most striking is the huge animal 

 whose skull, discovered by Mr. Darwin, was described by Professor 

 Owen under the name of Toxodonf, and since more fully investigated 

 by Dr. Burmeister^. Its Ungulate characters, however, much over- 

 weigh in importance those which it has in common with the Rodents; 

 and it may therefore be dismissed from present consideration. 



Another animal presenting an extraordinary combination of cha- 

 racters is that discovered by M. Bravard, and placed by him, under 

 the name of Typotherinm, among the Pachydermata§. Almost every 

 part of its skeleton has been obtained ; and the whole has been well 

 described by M. Serres|| under the name of Mesotherium, and by 

 Professor GervaisH under Bravard's name**. The last-named zoolo- 

 gist considers that it must be regarded as a link between the Rodents 

 and the Perissodactyles, and that its nearest affinities are with the 

 Leporidce. 



The most important characters in which Mesotherium differs 

 from existing Rodents are, briefly, the transversely hollowed crowns 

 of the incisors (which have not the chisel-edge so characteristic of 



* Cf. Turner, P. Z. S. 1848, p. 65. 



t Zoology of the 'Beagle,' pt. 1, pp. 16-35. 



I Ann. Mus. Pub. de Buenos Aires, i. pp. 254-286. 



§ Catalogue des especes d'anira. foss. recueillis dans l'Amer. du Sud, 4to. 

 Parana, I860. 



I| Conip. Eend. Ac. Paris, xliv. p. 961 (1857); kv. pp. 6, 17, 140-148, 

 273-279, 429-437, 593-599, 740-748, 841-848. 



^[ Zool. et Paleont. Generates, pp. 134-137, pis. xxii.-xxv. 



** M. Gervais regards Bravard's name as having priority ; on what grounds I 

 cannot discover. It does not appear whether or not it was used in the latter 

 writer's paper on the Geology of La Plata, published in the ' Registro Esta- 

 distico' of Buenos Ayres in 1857 (which M. Gervais was unable to find in Paris, 

 and which is not in the British Museum) ; but even if it was it would only be 

 contemporary with M. Serres's very appropriate name. 



